Pneumatic tires of the radial type comprise one or more plies of carcass reinforcing cords which extend from bead to bead in planes that contain the axis of the tire, or make a small angle therewith, and extend in a radial direction. The crown of the tire is provided with one or more belt plies, the cords of which extend at small bias angles relative to the circumferential center line of the tire. The large difference of angularity between the carcass reinforcing cords and the cords of the belt plies has generally required that these components be applied in two separate stages. Thus, the carcass ply or plies are assembled with bead cores in a first stage upon a generally cylindrical tire building drum after which the carcass is removed from the drum. In the second stage the cylindrical carcass is shaped to a generally toroidal configuration upon which the belt plies are applied, followed by the rubber which is to form the tread of the completed tire.
Efforts have been made heretofore to assemble radial tires completely in one stage upon a cylindrical tire building drum by providing a lubricant between those components of the tire which partake of the largest movements relative to each other during the shaping operation. Such lubricants have generally been provided in powdered or liquid form to select areas of the components during the tire building or assembling operation with other areas remaining untreated so that the assembled materials will adhere sufficiently for handling, while permitting the required relative movement during shaping. In such prior operations it has been difficult to properly control the application of the lubricant. This has resulted in high percentages of defective product as well as loss of time in cleaning the tire building apparatus to remove excess lubricant. Another method that has been used heretofor to produce radial tires in a single building process is described in U.S. Pat. No. 3,486,546. The method described in U.S. Pat. No. 3,486,546 is to use a material commonly referred to as "stretch cord" for the belt. The circumferentially extending belt is made from a plurality of plies of low bias angle which have initially a low tensile modulus until stretched a predetermined and limited amount and then abruptly change to a much higher modulus so that they become substantially inextensible. These cords of predetermined stretchability comprise textile yarns helically wrapped around a prevulcanized continuous core of elastomeric material with the size of the core and wrapping as well as the helical pitch of the latter so chosen that the cords become substantially inextensible after elongating in the range of 40-45% of their initial length.
Although the above two methods have been used heretofore, they both have disadvantages in that they result in high scrap tire rates and excess raw material waste. Nevertheless, there has been a continuing need for achieving one stage building of radial tires in order to reduce labor costs, increase output of existing equipment, and eliminate the need for specialized additional equipment required when two-stage building of the tire is employed.